Examine source code of Send to Kindle

{
  "manifest_version": 2,
  "name": "Send to Kindle",
  "version": "1.3",
  "description": "Push news articles, blogs posts and other web content to Kindle devices.",
  "homepage_url": "https://send.reabble.com",
  "icons": {
    "16": "icons/icon-16.png",
    "24": "icons/icon-24.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png",
    "128": "icons/icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "reabble.com@gmail.com",
      "strict_min_version": "60.0"
    }
  },
  "permissions": [
    "*://*.reabble.com/*",
    "*://*.reabble.cn/*",
    "activeTab",
    "notifications",
    "contextMenus"
  ],
  "browser_action": {
    "default_icon": {
      "16": "icons/icon-16.png",
      "24": "icons/icon-24.png",
      "32": "icons/icon-32.png",
      "48": "icons/icon-48.png",
      "96": "icons/icon-96.png",
      "128": "icons/icon-128.png"
    },
    "default_title": "Send to Kindle"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}